Mail gone after do-release-upgrade

I was running ubuntu 11.04 with ISPconfig setup on it (perfectserver).

I did a release upgrade from 11.04 to 12.04 and after that I was not able to access my imap (courier) server anymore.
I did a upgrade of ISPconfig and was able to access my mailbox again, but now it's empty. I hope it's looking in the wrong directory, but am not sure.

If I check mailbox quota from within ISPConfig it only has 26Kb used in my mail folder. This, to me, implicates that everything is gone.

And as a good home user I don't have a backup from the vmail folder.
So..... what to do now? I could connect the harddrive from my webserver to another machine and try to recover the data and afterwards copy it back to it's original location.